This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-277674, filed on Sep. 13, 2001, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photoelectric encoder, more particularly to an improvement to light-emitting and photoreceptive sections in the photoelectric encoder.
2. Description of the Related Art
A photoelectric encoder has been employed in a variety of machine tools and measuring instruments and the like, to detect a relative displacement between two relatively-moving members. The photoelectric encoder includes a light-emitting device such as an LED for emitting a beam of light to illuminate a scale. It also includes a photoreceptive device such as a photodiode for receiving the beam transmitted through, diffracted or reflected at the scale to detect an amount of a subjective displacement based on the condition of the received beam. In accordance with the need for downsizing an instrument that includes the photoelectric encoder mounted thereon, it is strongly desired to downsize the photoelectric encoder itself.
For the purpose of responding to the need, a known photoelectric encoder includes light-emitting devices and photoreceptive devices monolithically formed on the same IC substrate. Such the monolithic formation has a problem, however, because the yield of the whole product is influenced from both yields of the light-emitting and photoreceptive devices and accordingly lowered, resulting in a high price product. In addition, the monolithic formation possibly damages the light-emitting and photoreceptive devices if the devices contact with the scale because they oppose to the scale in a bare state.
On the other hand, there is another method of manufacturing light-emitting devices and photoreceptive devices individually followed by hybrid implementation. It is required in this case to prepare individual support members for the light-emitting devices and the photoreceptive devices, preventing the downsizing.
The present invention is provided with a photoelectric encoder, comprising: a reflective scale having predetermined reference gratings formed thereon; a flat illuminant having a flat surface emitting a beam of light to illuminate over said scale; a light transmissive member placed at a location between said flat illuminant and said reflective scale and closer to said flat illuminant; illuminant-side gratings formed at said light transmissive member and placed at front surface of said flat illuminant; and a photoreceptive device array consisting of a plurality of photoreceptive devices formed inside or outside of said light transmissive member for receiving said beam from said flat illuminant through said illuminant-side gratings and said reference gratings.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.